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Chronic stress from poverty, neglect and physical abuse in early life may shrink the parts of a child's developing brain responsible for memory, learning and processing emotion, researchers say.

While early life stress has already been linked to depression, anxiety, heart disease, cancer and a lack of educational and employment success, researchers have long sought to understand what part of the brain is affected to help guide interventions.

University of Wisconsin-Madison researchers published findings in the Biological Psychiatry journal that focused on two brain regions - the hippocampus and amygdala - involved in memory, learning and processing emotion.

Findings from other researchers have been mixed, which the UW researchers believe may be attributed to automated software used for brain measurements being prone to error as the brain regions are so small.

Co-leader of the study and UW professor of psychology Seth Pollak says his team recruited 128 children around the age of 12 and after extensive interviews documenting behavioural problems and their cumulative life stress divided them into four groups.

One group had experienced physical abuse, another was neglected before being adopted from a foreign country and a third came from low socioeconomic status households. The fourth group of children came from middle-class households and had not experienced any chronic early stress.

Researchers did MRI scans of the children's brains, focusing on the hippocampus and amygdala. They then traced by hand affected regions of the brain, which took almost two years.

"The regions are very small," one researcher said. "If you include even a little of one region that shouldn't be there, it skews the results."

The measurements showed that children who had experienced poverty, neglect or physical abuse had a smaller amygdala and hippocampus than the children from middle-class households, he said.

But why early life stress may shrink brain structures will require researchers to delve deeper into the circuitry of the brain and how its regions interact.